This invention relates generally to an epoxy resin composition and, more particularly, to a powder coating composition suitable for encapsulating or coating electric parts.
Electric parts such as ceramic condensers, resistor networks, hybrid IC and inductors are generally coated with or encapsulated in an insulating layer. Such an insulting coating is desired to exhibit good elasticity, adhesion strength, electrical insulation and resistance to heat, moisture and chemicals. Additionally, it is highly desirable that the insulation coating should show good "resistance to heat cycle", i.e. it should withstand a large number of repeated cycles of alternate hot and cold conditions.
One known epoxy resin powder coating composition for use in encapsulation of electric parts includes (a) an epoxy resin having a melting point of 50.degree.-150 .degree. C., (b) an acid anhydride hardener, (c) triphenyl phosphine as a curing accelerator, and (d) an inorganic filler (Japanese Published Unexamined Patent Application No. 61-89271). While this composition shows satisfactory resistance to heat and moisture, there involves a problem that the resistance to heat cycle is poor.
To improve resistance to heat cycle, there are proposals to use a flexible epoxy resin and an aliphatic acid anhydride hardener. While such a composition has an improved resistance to heat cycle, they are poor in resistance to heat and moisture.